Several control mechanisms of different design are used for manipulation with the stressing rod of stressing units. Most frequently, a balancing of the stressing rod by means of a counterweight suspended on a chain or a rope led over pulleys is used. Sometimes a pulley block, a hydraulic or pneumatic cylinder can be used instead of the counterweight. A direct connection of the stressing rod with a hand-operated wheel is mostly used for rotating this rod.
A considerable mass (up to the hundreds of kilograms), an enlarged construction height and increased inertial dynamic effects are disadvantages of the stressing unit containing the rod balanced by means of a counterweight. The necessity of controlling the revolving of the stressing rod which is parallel to the functional pulley block parts is a disadvantage of the pulleyblock system. The use of hydraulic and pneumatic cylinders increases the construction height and complicates the design of the controlling system for the distribution of pressure medium, the distribution itself so as the regulation of the pressure medium distribution. When using the rotation of the stressing rod by means of a hand-operated wheel, it is necessary to take into account a changed built-up area for screwing the stressing rod onto the stressed bolt, no gear ratio being usable for the revolving in order to reach the necessary rotation moment.